When using a MultiZoneUpdate, Tapestry will clear the referenced zone

Details

Description

I've spent all day chasing down an issue that appeared when we upgraded to Tapestry 5.2.1 - it doesn't occur with T5.2.0, and I finally managed to find the change that is causing the problem. It's the fix for TAP5-1177 where tapestry.js was changed from

The situation this is causing an issue for is where we have a form in a zone and submitting the form needs to update another zone so MultiZoneUpdate is used which has content in the json for the other zone. i.e.

{
"content" : "",
"zones" :

{
"someThingZone" : "<b>stuff</b>"
}

}

This used to leave the form inside it's zone alone which is good because some other javascript fires which accesses part of the form. If the form has been removed from the DOM (as happens with T5.2.1) then this Javascript fails. I'm not very familiar with this code, and I've not personally used MultiZoneUpdate, but it seems to me at first glance that the content bit of the json will always be "" for MultiZoneUpdate. All the content goes into the "zones" part of the json. Also, the comment in the T5.2.1 version seems to say that the content should be left alone if content is missing, but since missing is the same as "" it doesn't do that.

"I think Tapestry should not set the content property of the response when there's a MultiZoneUpdate response, so as to leave the Zone's current content unchanged." - HLS